Information processing device and method of controlling image forming apparatus

ABSTRACT

An information processing device includes: an acquisition unit configured to acquire color information on a specific color included in an inspection image, and a determination condition for determining a color shift with respect to the specific color; and a controller configured to: determine, based on the color information and the determination condition acquired by the acquisition unit, test image data representing a plurality of test images to be formed by an image forming apparatus; output the determined test image data to the image forming apparatus in order to form the plurality of test images; acquire luminance data on the plurality of test images, the luminance data being output from a color sensor; acquire spectral data on the plurality of test images, the spectral data being output from a spectroscopic sensor.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a technology of inspecting color of animage printed on a printed material.

Description of the Related Art

In an image forming apparatus for forming an image by employing anelectrophotographic process, characteristics in respective processes ofcharging, developing, transferring, and fixing change depending ontemporal changes and environmental changes. As a result, image densitiesor colors of a printed material may change. Accordingly, in the imageforming apparatus, image stabilizing control is performed. The imagestabilizing control is control involving detecting, by an opticalsensor, a detection image for detecting a density of an image formed onan image bearing member, and adjusting, based on a detection result, animage forming condition so that the image on the image bearing memberhas an appropriate image density. The image forming condition refers tovarious settings used at the time of image formation, such as a chargingamount of the image bearing member and a light emission energy amount oflaser for scanning the image bearing member.

The image stabilizing control is control for a process to be performedbefore the image is transferred onto a recording sheet. Thus, the imagestabilizing control cannot control the influence on the image density tobe caused in processes from the transferring process. For example, theimage stabilizing control cannot handle variations in transferefficiency to be caused by environmental variations in a case where atoner image is transferred from the image bearing member onto therecording sheet. Accordingly, the image density of the image to befinally formed on the recording sheet may have variations. In contrast,the image forming apparatus of Japanese Patent Application Laid-open No.2012-53089 causes an optical sensor to detect the detection image afterthe detection image is fixed to the recording sheet, and adjusts theimage forming condition based on the detection result, to therebysuppress the influence on the image density to be caused in theprocesses from the transferring process.

A corporate color to be used in, for example, a logo or a design mark ofa company is determined as an important component for identifying thecompany. Accordingly, a printed material including the corporate coloris required to be output so that, even when the color is unique, thecolor comes out as strictly determined. However, in the related art,calibration of color reproducibility is performed with reference to acolor having a high use frequency in the image to be printed, and henceit is difficult to strictly reproduce the specific color designated bythe user.

In recent years, there has been proposed a color inspecting system whichreads a color of an image of a printed material during printing andinspects the color of the read color. In United States PatentApplication Publication No. 2012/0327435 A1, there is disclosed an imageforming apparatus for performing a color inspection. This image formingapparatus prints, on the recording sheet, a measurement patch formeasuring a specific color designated by the user. The image formingapparatus performs the color stabilizing control based on results ofmeasuring the color of the measurement patch by an image sensor. In acase where the results of measuring the color are outside of anallowable range, the image forming apparatus notifies the user of thisfact, and performs the color stabilizing control again.

The image sensor to be used for measuring the color of the image printedon the printed material outputs, as the color measurement results,luminance values (RGB data) of three colors of red (R), green (G), andblue (B). This RGB data is converted into spectral data formed of L*,a*, b* of the CIELab color space. For the conversion of the RGB datainto the CIELab color space, a color conversion table being a look-uptable is used. In the color conversion table, in general, not all colorconversion values (Lab values) for all input values (luminance values ofR, G, and B) are registered, but color conversion values at only aplurality of grid points regularly arranged in an input color space areregistered. In a case where such a color conversion table is used toperform the color conversion, the color conversion values other than thegrid points are obtained through interpolation operation performed basedon the color conversion values registered at the grid points (JapanesePatent Application Laid-open No. 2002-64719).

As the image sensor, an optical sensor is frequently used. The opticalsensor generates output values from light received via color filters ofred (R), green (G), and blue (B) having sensitivities different fromthat of the sense of sight of human. Accordingly, in a case where theoptical sensor is used to perform the color measurement, depending onthe color, it is difficult for the optical sensor to perform the colormeasurement with desired accuracy. This also affects the results of thecolor inspection. Accordingly, there has been a demand for an imageforming apparatus capable of performing color measurement of an image tobe used for color inspection with high accuracy.

Further, the color conversion using the color conversion table isperformed by a method of performing conversion into the Lab valuesthroughout the entire color gamut that can be expressed by the threecolors of R, G, and B. With this method, the entire color gamut issubjected to the color conversion at a level free from strangeness.However, in a color gamut in which Lab is liable to change with respectto each color in RGB data, a conversion error is increased, and highlyaccurate color inspection becomes difficult. Accordingly, there has beena demand for an image forming apparatus capable of inspecting the colorwith high accuracy.

SUMMARY OF THE INVENTION

An information processing device according to the present disclosureincludes:

an acquisition unit configured to acquire color information on aspecific color included in an inspection image, and a determinationcondition for determining a color shift with respect to the specificcolor; and a controller configured to: determine, based on the colorinformation and the determination condition acquired by the acquisitionunit, test image data indicating a plurality of test images to be formedby an image forming apparatus; output the determined test image data tothe image forming apparatus in order to form the plurality of testimages; acquire luminance data on the plurality of test images, theluminance data being output from a color sensor; acquire spectral dataon the plurality of test images, the spectral data being output from aspectroscopic sensor; generate, based on the spectral data and theluminance data, a conversion condition for converting a reading resultobtained by the color sensor; acquire luminance data on an image to beformed by the image forming apparatus, the luminance data on the imageto be formed by the image forming apparatus being output from the colorsensor; convert, based on the conversion condition, the luminance dataon the image to be formed by the image forming apparatus; and determine,based on converted luminance data and the determination condition, thecolor shift with respect to the specific color in the inspection image,wherein the plurality of test images include a first test image of afirst color in which a color difference from the specific color has afirst value, and a second test image of a second color in which thecolor difference from the specific color has a second value, wherein thefirst value is smaller than a value of the color differencecorresponding to the determination condition, and wherein the secondvalue is larger than the value of the color difference corresponding tothe determination condition.

A method of controlling an image forming apparatus for forming an imageto a sheet according to the present disclosure includes: a firstacquisition step of acquiring color information on a specific colorincluded in an inspection image; a second acquisition step of acquiringa determination condition for determining a color shift with respect tothe specific color; a determination step of determining, based on thecolor information and the determination condition, test image datarepresenting a plurality of test images; a test print step of printingthe plurality of test images based on the test image data; a firstreading step of reading the plurality of test images by a color sensor,the color sensor being configured to receive reflected light from ameasurement target and output red luminance data, green luminance data,and blue luminance data on the measurement target; a second reading stepof reading the plurality of test images by a spectroscopic sensor, thespectroscopic sensor being configured to receive the reflected lightfrom the measurement target, detect a light intensity of each of aplurality of wavelengths which are more than 3 for the measurementtarget, and output spectral data based on the light intensity of each ofthe plurality of wavelengths; a generation step of generating, based onthe spectral data and the luminance data, a conversion condition forconverting a reading result obtained by the color sensor; a print stepof printing the inspection image; a third reading step of reading theinspection image by the color sensor; a conversion step of convertingthe luminance data on the inspection image based on the conversioncondition; and a determination step of determining, based on convertedluminance data and the determination condition, the color shift withrespect to the specific color in the inspection image, wherein theplurality of test images include a first test image of a first color inwhich a color difference from the specific color has a first value, anda second test image of a second color in which the color difference fromthe specific color has a second value, wherein the first value issmaller than a value of the color difference corresponding to thedetermination condition, and wherein the second value is larger than thevalue of the color difference corresponding to the determinationcondition.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram of a configuration of a printingsystem.

FIG. 2 is a view of a configuration of an image forming apparatus.

FIG. 3 is an explanatory diagram of a configuration of a reader.

FIG. 4 is an explanatory view of a configuration of a line sensor.

FIG. 5 is an explanatory diagram of a configuration of a spectroscopicsensor unit.

FIG. 6 is a flow chart for illustrating print processing including colorinspection processing.

FIG. 7 is a diagram of an example of a color calibration chart.

FIG. 8 is a flow chart for illustrating color calibration processing.

FIG. 9 is an explanatory diagram of a method of calculating L*, a*, b*of surrounding colors of a specific color.

FIG. 10A and FIG. 10B are explanatory diagrams of a color conversionlook-up table.

FIG. 11 is a diagram of an example of the color calibration chart.

FIG. 12 is a flow chart for illustrating the color calibrationprocessing.

FIG. 13 is an explanatory diagram of the method of calculating L*, a*,b* of the surrounding colors of the specific color.

DESCRIPTION OF THE EMBODIMENTS

Now, embodiments of the present disclosure are described in detail withreference to the drawings. However, the following embodiments are not tolimit the disclosure laid down in the scope of patent claims, and notall of combinations of features described in the embodiments areindispensable to the solving means of the present disclosure.

First Embodiment

<Printing System>

FIG. 1 is an explanatory diagram of a configuration of a printingsystem. The printing system includes an image forming apparatus 100 anda host computer 101. The image forming apparatus 100 and the hostcomputer 101 are communicably connected through a network 105. Thenetwork 105 is formed of a communication line such as a local areanetwork (LAN), a wide area network (WAN), or a public communicationline. A plurality of the image forming apparatus 100 and a plurality ofthe host computers 101 may be connected to the network 105.

The host computer 101 is, for example, a server apparatus, and transmitsa print job to the image forming apparatus 100 through the network 105.A print job includes various kinds of printing information required forprinting, such as image data, the type of recording sheet to be used inprinting, the number of sheets to be printed, and an instruction toperform double-sided printing or single-sided printing.

The image forming apparatus 100 includes a controller 110, an operationpanel 120, a sheet feeding portion 140, a printer 150, and a reader 160.The controller 110, the operation panel 120, the sheet feeding portion140, the printer 150, and the reader 160 are connected to becommunicable to/from one another through a system bus 116. The imageforming apparatus 100 controls operation of the printer 150 based on theprint job acquired from the host computer 101 to form an image based onthe image data on a recording sheet.

The controller 110 controls operations of respective units of the imageforming apparatus 100. The controller 110 is an information processingdevice including a read only memory (ROM) 112, a random access memory(RAM) 113, and a central processing unit (CPU) 114. The controller 110includes a communication control unit 111, and a storage 115. Modulesare connected to be communicable to/from one another through the systembus 116.

The communication control unit 111 is a communication interface forperforming communication to/from the host computer 101 and other devicesthrough the network 105. The storage 115 is a mass storage device formedof, for example, a hard disk drive (HDD) or a solid state drive (SSD).The storage 115 stores a computer program and various kinds of data usedin image forming processing (print processing). The CPU 114 executes acomputer program stored in the ROM 112 or the storage 115 to controloperation of the image forming apparatus 100. The RAM 113 provides awork area used by the CPU 114 in executing the computer program.

The operation panel 120 is a user interface, and includes an inputinterface and an output interface. The input interface includes, forexample, operation buttons, numeric keys, or a touch panel. The outputinterface includes, for example, a liquid crystal display (LCD) or otherdisplays, or a loudspeaker. A user can input a print job, a command, andprint settings, for example, to the image forming apparatus 100 throughthe operation panel 120. The operation panel 120 displays a settingscreen and a status of the image forming apparatus 100 on the display.

The sheet feeding portion 140 includes a plurality of sheet feedingstages for containing recording sheets, which are to be described later.The sheet feeding portion 140 feeds the recording sheet of the typespecified in the print job from a sheet feeding stage containing therecording sheet. The sheet feeding stage contains a plurality ofrecording sheets (recording sheet bundle), and the sheet feeding portion140 feeds recording sheets in order from a recording sheet at the top.The sheet feeding portion 140 conveys the recording sheet fed from thesheet feeding stage to the printer 150. The respective sheet feedingstages may contain recording sheets of the same type, or may containrecording sheets of different types.

The printer 150 prints an image on the recording sheet fed from thesheet feeding portion 140 based on the image data included in the printjob, to thereby generate a printed material. The reader 160 is an imagereading apparatus for reading images from the printed material generatedby the printer 150, and transmitting a reading result to the controller110. The images read by the reader 160 are images (detection images) foradjusting an image forming condition to be used when the printer 150forms an image. The controller 110 detects states of the images such asimage quality from a result of reading the detection images by thereader 160, and adjusts the image forming condition based on thedetected states of the images. In the first embodiment, the controller110 detects the image densities from the detection images, and the imageforming condition is adjusted based on the detected image densities.

<Image Forming Apparatus>

FIG. 2 is a view of a configuration of the image forming apparatus 100.The image forming apparatus 100 includes, in order from an upstream sidein a conveying direction of the recording sheet, sheet feeding stages140 a to 140 e, the printer 150, the reader 160, and a finisher 190. Thesheet feeding stages 140 a to 140 e form the sheet feeding portion 140.The finisher 190 is a post-processing apparatus for performingpost-processing on the printed material generated by the printer 150.The finisher 190 performs, for example, stapling and sorting on aplurality of printed materials.

The printer 150 includes a plurality of image forming units 222 forforming images of different colors, respectively. The printer 150 in thefirst embodiment includes four image forming units 222 in order to formimages of four colors: yellow (Y), magenta (M), cyan (C), and black (K).The image forming units 222 are different only in color of the images tobe formed, and perform a similar operation with a similar configuration.

One image forming unit 222 includes a photosensitive drum 153, acharging device 220, an exposure device 223, and a developing device152. The photosensitive drum 153 is a drum-shaped photosensitive memberhaving a photosensitive layer on a surface thereof, and is driven torotate in a direction of an arrow R1 by a motor (not shown). Thecharging device 220 charges the surface (photosensitive layer) of therotating photosensitive drum 153. The exposure device 223 exposes thecharged surface of the photosensitive drum 153 with laser light. Thelaser light scans the surface of the photosensitive drum 153 in an axialdirection of the photosensitive drum 153. The direction in which thelaser light scans the surface of the photosensitive drum 153 is a mainscanning direction of the printer 150 (depth direction of FIG. 2 ). As aresult, an electrostatic latent image is formed on the surface of thephotosensitive drum 153. The developing device 152 develops theelectrostatic latent image with the use of a developer (toner). As aresult, an image (toner image) obtained by visualizing the electrostaticlatent image is formed on the surface of the photosensitive drum 153.

The printer 150 includes an intermediate transfer belt 154 to whichtoner images generated by the respective image forming units 222 aretransferred. The intermediate transfer belt 154 is driven to rotate in adirection of an arrow R2. The toner images of the respective colors aretransferred at timings corresponding to the rotation of the intermediatetransfer belt 154. As a result, a full-color toner image obtained bysuperimposing the toner images of the respective colors on one anotheris formed on the intermediate transfer belt 154. The full-color tonerimage is conveyed, with the rotation of the intermediate transfer belt154, to a nip portion formed by the intermediate transfer belt 154 andtransfer rollers 221. The full-color toner image is transferred onto therecording sheet by the nip portion.

Recording sheets are contained in the sheet feeding stages 140 a, 140 b,140 c, 140 d, and 140 e of the sheet feeding portion 140, and are fed inaccordance with timings at which the images are formed by the imageforming units 222. A sheet feeding stage to feed a recording sheet isinstructed by the print job. The recording sheet is conveyed to the nipportion formed by the intermediate transfer belt 154 and the transferrollers 221 at a timing when the full-color toner image is conveyed tothe nip portion. As a result, the toner image is transferred at apredetermined position of the recording sheet. The conveying directionof the recording sheet is a sub-scanning direction, which is orthogonalto the main scanning direction.

The printer 150 includes a first fixing device 155 and a second fixingdevice 156, each of which fixes a toner image on the recording sheet byheating and pressurizing. The first fixing device 155 includes a fixingroller including a heater, and a pressure belt for bringing therecording sheet into pressure contact with the fixing roller. The fixingroller and the pressure belt are driven by a motor (not shown) to pinchand convey the recording sheet. The second fixing device 156 is arrangedon a downstream side of the first fixing device in the conveyingdirection of the recording sheet. The second fixing device 156 is usedto increase gloss and ensure fixability for the image on the recordingsheet that has passed through the first fixing device 155. The secondfixing device 156 includes a fixing roller including a heater, and apressure roller including a heater. Depending on the type of therecording sheet, the second fixing device 156 is not used. In this case,the recording sheet is not conveyed to the second fixing device 156, butis conveyed to a conveyance path 130. To that end, on the downstreamside of the first fixing device 155, there is provided a flapper 131 forguiding the recording sheet to any one of the conveyance path 130 andthe second fixing device 156.

On the downstream side of a position at which the conveyance path 130merges on the downstream side of the second fixing device 156, aconveyance path 135 and a discharge path 139 are provided. Therefore, atthe position at which the conveyance path 130 merges on the downstreamside of the second fixing device 156, there is provided a flapper 132for guiding the recording sheet to any one of the conveyance path 135and the discharge path 139. The flapper 132 guides, for example, in adouble-sided printing mode, the recording sheet having an image formedon a first surface thereof to the conveyance path 135. The flapper 132guides, for example, in a face-up discharge mode, the recording sheethaving the image formed on the first surface thereof to the dischargepath 139. The flapper 132 guides, for example, in a face-down dischargemode, the recording sheet having the image formed on the first surfacethereof to the conveyance path 135.

The recording sheet conveyed to the conveyance path 135 is conveyed to areversing portion 136. The recording sheet conveyed to the reversingportion 136 has the conveying direction reversed after the conveyingoperation is stopped once. The recording sheet is guided from thereversing portion 136 to any one of the conveyance path 135 and aconveyance path 138 by a flapper 133. The flapper 133 guides, forexample, in the double-sided printing mode, the recording sheet havingthe conveying direction reversed to the conveyance path 138 in order toprint an image on a second surface. The recording sheet conveyed to theconveyance path 138 is conveyed toward the nip portion between theintermediate transfer belt 154 and the transfer rollers 221. As aresult, front and back sides of the recording sheet at the time ofpassing through the nip portion are reversed, and the image is formed onthe second surface. The flapper 133 guides, for example, in theface-down discharge mode, the recording sheet having the conveyingdirection reversed to the conveyance path 135. The recording sheetconveyed to the conveyance path 135 by the flapper 133 is guided to thedischarge path 139 by a flapper 134.

The recording sheet having the images formed thereon by the printer 150is conveyed from the discharge path 139 to the reader 160. The reader160 is an image reading apparatus for performing color measurement of auser image printed on the recording sheet in accordance with the printjob, and reading the image density of the detection image printed on therecording sheet. The recording sheet conveyed from the printer 150 tothe reader 160 is conveyed along a conveyance path 313 included in thereader 160. The reader 160 includes an original detection sensor 311, aline sensor unit 312, and a spectroscopic sensor unit 315 on theconveyance path 313. Between the line sensor unit 312 and the conveyancepath 313, a flow reading glass 314 is arranged. At a position opposed tothe spectroscopic sensor unit 315 across the conveyance path 313, awhite plate 316 is arranged. The reader 160 performs color measurementby the line sensor unit 312 and the spectroscopic sensor unit 315 whileconveying the recording sheet having the images printed thereon by theprinter 150 along the conveyance path 313.

The original detection sensor 311 is, for example, an optical sensorincluding a light emitting element and a light receiving element. Theoriginal detection sensor 311 detects a leading edge in the conveyingdirection of the recording sheet conveyed along the conveyance path 313.A result of detecting the leading edge of the recording sheet by theoriginal detection sensor 311 is transmitted to the controller 110. Thecontroller 110 starts operation of reading by the reader 160 (linesensor unit 312 and spectroscopic sensor unit 315) based on a timingwhen the leading edge of the recording sheet is detected by the originaldetection sensor 311. The line sensor unit 312 is an optical sensorprovided on the side of the recording sheet surface on which the imagesare formed, so as to read the detection image printed on the recordingsheet being conveyed. The spectroscopic sensor unit 315 is provided onthe side of the recording sheet surface on which the images are formed,so as to be driven in the main scanning direction to measure the colorsof the images formed on the recording sheet.

<Reader>

FIG. 3 is an explanatory diagram of a configuration of the reader 160.The reader 160 includes, in addition to the line sensor unit 312, thespectroscopic sensor unit 315, and the original detection sensor 311, animage memory 303 and a color detection processing unit 305. Operationsof the line sensor unit 312, the spectroscopic sensor unit 315, theimage memory 303, the color detection processing unit 305, and theoriginal detection sensor 311 are controlled by the CPU 114 of thecontroller 110.

The line sensor unit 312 includes a line sensor 301, a memory 300, andan A/D converter 302. The line sensor 301 is, for example, a contactimage sensor (CIS). The line sensor 301 is a color sensor formed oflight receiving elements including respective color filters of red,green, and blue. The light receiving element including the red colorfilter mainly receives light of 630 nm in reflected light from ameasurement target, and outputs a signal that is based on the luminancevalue of the light of 630 nm. The light receiving element including thegreen color filter mainly receives light of 530 nm in the reflectedlight from the measurement target, and outputs a signal that is based onthe luminance value of the light of 530 nm. The light receiving elementincluding the blue color filter mainly receives light of 440 nm in thereflected light from the measurement target, and outputs a signal thatis based on the luminance value of the light of 440 nm. In the memory300, correction information, such as light amount variations betweenpixels of the line sensor 301, a level difference between the pixels,and a distance between the pixels, is stored. The A/D converter 302acquires an analog signal being a reading result obtained by the linesensor 301. The A/D converter 302 converts the acquired analog signalinto a digital signal, and transmits the digital signal to the colordetection processing unit 305. The digital signal is read data(luminance data) of red (R), green (G), and blue (B).

The spectroscopic sensor unit 315 includes a spectroscopic sensor 306, amemory 304, an A/D converter 307, and a spectroscopic sensor drive unit308. The spectroscopic sensor 306 is formed of, for example, a lightsource, a lens, a diffraction grating surface, and a light receivingportion. The light receiving portion is, for example, a CMOS sensor. Thespectroscopic sensor 306 irradiates the measurement target with lightfrom the light source, and disperses the reflected light for eachwavelength by the diffraction grating. The spectroscopic sensor 306receives the light dispersed for each wavelength at pixels provided inthe light receiving portion separately for each wavelength, and performsphotoelectric conversion into a voltage value of each wavelength. Thelight receiving portion of the spectroscopic sensor 306 receives, forexample, light of from 380 nm to 780 nm with the light being dividedinto wavelengths in units of 10 nm. The light receiving portion outputsa voltage that is based on a light intensity of each wavelength as ananalog signal. The output value of the light of each wavelength, whichhas been converted into a voltage value, is an analog signal. The A/Dconverter 307 converts this analog signal into a digital signal, andtransmits the digital signal to the color detection processing unit 305as spectral data. In the memory 304, various kinds of correctioninformation, such as stray light data and dark current data of thespectroscopic sensor 306, are stored. The spectroscopic sensor driveunit 308 is a drive source for driving the spectroscopic sensor unit 315in the main scanning direction.

The color detection processing unit 305 is formed of a semiconductordevice, such as a field-programmable gate array (FPGA) or an applicationspecific integrated circuit (ASIC). The color detection processing unit305 derives average values (average luminance values (R_(A), G_(A),B_(A))) of the luminance values of the respective colors (each of RGB)in a color measurement region (detection image part) from the luminancedata of RGB acquired from the line sensor unit 312, and transmits theaverage values to the CPU 114. The CPU 114 includes a color conversionlook-up table LUT_(IN) for converting the luminance values (RGB data) ofthe respective colors of RGB into L*, a*, b* values. The CPU 114 usesthe color conversion look-up table LUT_(IN) to convert the averageluminance values (R_(A), G_(A), B_(A)) of the respective colors into theL_(a)*, a_(a)*, b_(a)* values. The color detection processing unit 305calculates the L*, a*, b* values from the spectral data acquired fromthe spectroscopic sensor unit 315. The color detection processing unit305 outputs the calculated L*, a*, b* values to the CPU 114.

Operations of the line sensor unit 312, the spectroscopic sensor unit315, the image memory 303, the color detection processing unit 305, andthe original detection sensor 311 are controlled by the CPU 114 of thecontroller 110. The image memory 303 stores image data required forimage processing performed by the CPU 114.

<Line Sensor>

FIG. 4 is an explanatory diagram of a configuration of the line sensor301. The line sensor 301 includes light emitting portions 400 a and 400b, light guiding members 402 a and 402 b, a lens array 403, and a sensorchip group 401. The line sensor 301 has a substantially rectangularparallelepiped shape, and reads an image with a longitudinal directionthereof being a main scanning direction.

Each of the light emitting portions 400 a and 400 b is, for example, alight source formed of a light emitting diode (LED) that emits whitelight. The light guiding member 402 a has the light emitting portion 400a arranged in an end portion thereof, and irradiates the recording sheetwith light emitted from the light emitting portion 400 a. The lightguiding member 402 b has the light emitting portion 400 b arranged at anend thereof, and irradiates the recording sheet with light emitted fromthe light emitting portion 400 b. Each of the light guiding members 402a and 402 b is formed in straight line in the main scanning direction.Therefore, the line sensor 301 irradiates the recording sheet with lightin line in the main scanning direction. The main scanning direction ofthe line sensor unit 312 and the main scanning direction of the printer150 are the same direction.

The lens array 403 is an optical system for guiding reflected light fromthe recording sheet of the light irradiated from the light emittingportions 400 a and 400 b to the sensor chip group 401. The sensor chipgroup 401 is formed of a plurality of photoelectric conversion elements(sensor chips) arrayed in line in the main scanning direction. Onesensor chip reads an image of one pixel. The plurality of sensor chipsin the first embodiment have a three-line configuration. One line iscoated with a red (R) color filter, other one line is coated with agreen (G) color filter, and the other one line is coated with a blue (B)color filter. The light guided by the lens array 403 forms an image on alight receiving surface of each sensor chip of the sensor chip group401.

The light emitted from the light emitting portions 400 a and 400 b isdiffused inside the light guiding members 402 a and 402 b, and is outputfrom a portion having a curvature to illuminate the entire area in themain scanning direction of the recording sheet. The light guiding member402 a and the light guiding member 402 b are arranged across the lensarray 403 in a sub-scanning direction, which is orthogonal to the mainscanning direction. Therefore, the line sensor 301 has a both-sideillumination configuration in which the lens array 403 (image readingline) is irradiated with light from two directions of the sub-scanningdirection. The sub-scanning direction of the line sensor unit 312 andthe sub-scanning direction of the printer 150 are the same direction.

<Spectroscopic Sensor Unit>

FIG. 5 is an explanatory diagram of a configuration of the spectroscopicsensor unit 315. The spectroscopic sensor unit 315 has a substantiallyrectangular parallelepiped shape with a longitudinal direction thereofbeing the main scanning direction. The recording sheet is conveyed inthe sub-scanning direction on the depth side of the spectroscopic sensorunit 315 of FIG. 5 . The spectroscopic sensor 306, the memory 304, andthe A/D converter 307 are integrally formed. The A/D converter 307 isconnected to the color detection processing unit 305 through a wiringline such as a flexible flat cable (not shown).

The spectroscopic sensor 306 is provided on a rail 309 extending fromthe spectroscopic sensor drive unit 308 in the main scanning direction.The spectroscopic sensor 306 is moved on the rail 309 by thespectroscopic sensor drive unit 308. The spectroscopic sensor drive unit308 incorporates a stepping motor, and is controlled based on theinstruction from the CPU 114. The spectroscopic sensor drive unit 308can move the spectroscopic sensor 306 to a predetermined position in themain scanning direction with high accuracy.

On the outer side of a region (conveyance region) in which thespectroscopic sensor unit 315 can read the recording sheet, a homeposition HP is provided. The white plate 316 is arranged at the homeposition HP. The recording sheet is conveyed line by line in thesub-scanning direction, and is brought into a stop state at the timingof color measurement. The spectroscopic sensor unit 315 has an openingportion 310 at a position corresponding to the conveyance region. Thespectroscopic sensor 306 reads the recording sheet through the openingportion 310.

The spectroscopic sensor 306 is positioned at the home position HPbefore the color measurement is started. In a case where an instructionto start the color measurement is given from the CPU 114, thespectroscopic sensor 306 reads the white plate 316 so as to performcalibration, such as light source light amount adjustment or whitereference matching. The spectroscopic sensor 306 starts to move in themain scanning direction at an equal speed from the home position HPafter the calibration, and starts color measurement of one line inresponse to detection of a trigger patch being a trigger. In a casewhere the spectroscopic sensor 306 ends the color measurement of oneline, the spectroscopic sensor 306 returns to the home position HP.After that, after the recording sheet is moved for one line in thesub-scanning direction, the spectroscopic sensor 306 starts to move inthe main scanning direction again to perform color measurement for oneline. Such movement of the recording sheet for one line and colormeasurement of the spectroscopic sensor 306 for one line are repeated sothat the color measurement of one recording sheet is performed.

<Color Inspection>

FIG. 6 is a flow chart for illustrating print processing including colorinspection processing. This processing is started when the user inputsan instruction of color inspection through the operation panel 120 so asto input an instruction to start the copy. The instruction of colorinspection includes, for example, a recording sheet size, a print mode,the number P_(MAX) of sheets to be printed, color values (specificcolor: L₀₀*, a₀₀*, b₀₀*) for which the color inspection is desired, acolor inspection designation region (region X=X_(S) to X_(E), Y=Y_(S) toY_(E) on the sheet), and a color inspection threshold value Cth.

The CPU 114 acquires the instruction of color inspection from theoperation panel 120, and performs, based on the instruction, setting ofinformation required for the print job to each apparatus, and storing ofvarious parameters included in the instruction into the RAM 113, tothereby perform mode setting (Step S600). The CPU 114 waits for a copystart instruction from the operation panel 120 after the mode setting isperformed (Step S601: N).

After the CPU 114 acquires the copy start instruction (Step S601: Y),the CPU 114 performs color calibration of the line sensor 301 inaccordance with the contents of the instruction of color inspection, andcreates a color calibration matrix M of the line sensor 301 (Step S602).The color calibration matrix M is a conversion condition for converting,for the color calibration, L*, a*, b* converted from the reading resultsobtained by the line sensor unit 312 into color values. Details of theprocess step of Step S602 are described later. The CPU 114 initializes aprint count value P to “0” after the color calibration is performed(Step S603). The print count value P represents the number of recordingsheets having the images formed thereon by the printer 150.

The CPU 114 causes the printer 150 to perform print processing ofprinting an inspection image including a specific color under acondition corresponding to the instruction of color inspection, andgenerates a printed material (Step S604). The CPU 114 causes the linesensor unit 312 to perform color measurement of the printed material(Step S605). The color measurement is performed with respect to thecolor inspection designation region (region X=X_(S) to X_(E), Y=Y_(S) toY_(E) on the sheet) of the printed material. As the result of the colormeasurement of the printed material, the luminance data of RGB istransmitted from the line sensor unit 312 to the color detectionprocessing unit 305. The color detection processing unit 305 derives theaverage luminance values (R_(A), G_(A), B_(A)) of the respective colorsof RGB in the color measurement region from the luminance data of RGBacquired from the line sensor unit 312, and transmits the averageluminance values to the CPU 114.

The CPU 114 includes a color conversion look-up table LUT_(IN) forconverting the luminance values (RGB data) of the respective colors ofRGB into L*, a*, b* values. The CPU 114 uses the color conversionlook-up table LUT_(IN) to convert the average luminance values (R_(A),G_(A), B_(A)) of the respective colors into the L_(a)*, a_(a)*, b_(a)*values. The CPU 114 uses the color calibration matrix M created in theprocess step of Step S602 to derive the color values (L_(Pa*), a_(Pa*),b_(Pa*)) from the results of conversion from the average luminancevalues (R_(A), G_(A), B_(A)) to the L_(a)*, a_(a)*, b_(a)* values.

The CPU 114 derives a color difference ΔE00 between the color values(L_(Pa*), a_(Pa*), b_(Pa*)) obtained as the results of the colormeasurement and the color values (L₀₀*, a₀₀*, b₀₀*) serving as colorinformation on the specific color (Step S606). The CPU 114 compares thederived color difference ΔE00 with the color inspection threshold valueCth serving as a determination condition (Step S607). The result of thecolor inspection is determined based on the result of comparison betweenthe color difference ΔE00 and the color inspection threshold value Cth.

In a case where the color difference ΔE00 is equal to or smaller thanthe color inspection threshold value Cth (Step S607: Y), the CPU 114determines that a difference between the specific color of the imageprinted on the recording sheet and the designated specific color forwhich the color inspection is desired is small. In this case, the CPU114 increments the print count value P by 1 because the printing isnormally performed in the specific color (Step S608). The CPU 114determines whether or not the print count value P has reached the numberP_(MAX) of sheets to be printed (Step S610). In a case where the printcount value P has not reached the number P_(MAX) of sheets to be printed(Step S610: N), the CPU 114 repeats the process steps of Step S604 andthereafter until the print count value P reaches the number P_(MAX) ofsheets to be printed. In a case where the print count value P hasreached the number P_(MAX) of sheets to be printed (Step S610: Y), theCPU 114 ends the print processing including the color inspectionprocessing.

In a case where the color difference ΔE00 is larger than the colorinspection threshold value Cth (Step S607: N), the CPU 114 determinesthat the difference between the specific color of the image printed onthe recording sheet and the designated specific color for which thecolor inspection is desired is large. In this case, the CPU 114 causesthe operation panel 120 to display a warning because the printing is notnormally performed in the specific color (Step S609). The display of thewarning indicates that the color inspection designation region has acolor separated from the specific color L₀₀*, a₀₀*, b₀₀* by an amountlarger than an allowable color difference (color inspection thresholdvalue Cth), and the result of the color inspection is inappropriate. Thewarning may be performed through generation of sounds from a speaker inaddition to the indication on the display. After the CPU 114 performsthe display of the warning, the CPU 114 ends the print processingincluding the color inspection processing.

<Color Calibration Processing>

The color calibration processing of Step S602 is described. FIG. 7 is adiagram of an example of a color calibration chart to be used in thecolor calibration processing of the line sensor unit 312. A colorcalibration chart 501 is created by printing 98 patch images 504 as thedetection image on a recording sheet that is long in the sub-scanningdirection. The patch images 504 are arranged in 7 rows and 14 columns inthe main scanning direction and the sub-scanning direction,respectively. At a left end of the color calibration chart 501 in themain scanning direction, a margin 502 is provided. On the right side ofthe margin 502, a black trigger patch 503 is provided. On the right sideof the trigger patch 503, the 98 patch images 504 are provided. The 98patch images 504 for color calibration include 49 patch images writtenas “Axx” and 49 patch images written as “Pxx.”

The 49 patch images 504 written as “Axx” are images obtained throughprimary selection of image density values corresponding to the specificcolor L₀₀*, a₀₀*, b₀₀* and the L*, a*, b* values of surrounding colorscalculated as values separated by predetermined color differences fromthe specific color L₀₀*, a₀₀*, b₀₀*. In this case, the image densityvalues are referred to as “YMCK values.” In FIG. 7 , the middle patchimage is an image having the YMCK values of the specific color L₀₀*,a₀₀*, b₀₀*. The YMCK values are set for each of the colors of yellow(Y), magenta (M), cyan (C), and black (K).

The 49 patch images 504 written as “Pxx” are images obtained throughsecondary selection of YMCK values corresponding to the specific colorL₀₀*, a₀₀*, b₀₀* and the L*, a*, b* values of surrounding colorscalculated as values separated by predetermined color differences fromthe specific color L₀₀*, a₀₀*, b₀₀*. The primary selection and thesecondary selection have different selection criteria.

The method of selecting the YMCK values with respect to the L*, a*, b*values of the 98 patch images 504 is described later. The positions atwhich the patch images 504 of the color calibration chart 501 are formedare not limited to those of FIG. 7 .

FIG. 8 is a flow chart for illustrating the color calibrationprocessing. FIG. 9 is an explanatory diagram of a method of calculatingL*, a*, b* of the surrounding colors of the specific color. FIG. 10A andFIG. 10B are explanatory diagrams of a color conversion look-up tableLUT_(OUT) for performing color conversion from the L*, a*, b* values tothe YMCK values.

The CPU 114 calculates L*, a*, b* of the surrounding colors from thespecific color L₀₀*, a₀₀*, b₀₀* (Step S800). For the calculation, theCPU 114 first acquires the specific color L₀₀*, a₀₀*, b₀₀* from the RAM113. The CPU 114 calculates the surrounding colors separated bypredetermined color differences from the specific color L₀₀*, a₀₀*,b₀₀*. For example, as illustrated in FIG. 9 , 48 surrounding colors areselected. The CPU 114 calculates L*, a*, b* of the following 48surrounding colors corresponding to ΔE00=2, 4, 6, 8, 10, 12 as thepredetermined color differences.

-   -   Surrounding color 01 to surrounding color 08 separated in color        by color difference ΔE00=2        -   L*, a*, b*=L₀₁*, a₀₁*, b₀₁* to L₀₈*, a₀₈*, b₀₈*    -   Surrounding color 09 to surrounding color 16 separated in color        by color difference ΔE00=4        -   L*, a*, b*=L₀₉*, a₀₉*, b₀₉* to L₁₆*, a₁₆*, b₁₆*    -   Surrounding color 17 to surrounding color 24 separated in color        by color difference ΔE00=6        -   L*, a*, b*=L₁₇*, a₁₇*, b₁₇* to L₂₄*, a₂₄*, b₂₄*    -   Surrounding color 25 to surrounding color 32 separated in color        by color difference ΔE00=8        -   L*, a*, b*=L₂₅*, a₂₅*, b₂₅* to L₃₂*, a₃₂*, b₃₂*    -   Surrounding color 33 to surrounding color 40 separated in color        by color difference ΔE00=10        -   L*, a*, b*=L₃₃*, a₃₃*, b₃₃* to L₄₀*, a₄₀*, b₄₀*    -   Surrounding color 41 to surrounding color 48 separated in color        by color difference ΔE00=12        -   L*, a*, b*=L₄₁*, a₄₁*, b₄₁* to L₄₈*, a₄₈*, b₄₈*

The CPU 114 calculates patch colors being colors of the patch images tobe used in the color calibration chart 501 (performs primary selection)(Step S801). The patch colors are the image density values (YMCKvalues). The CPU 114 converts L₀₀*, a₀₀*, b₀₀* to L₄₈*, a₄₈*, b₄₈*calculated in the process step of Step S800 based on the colorconversion look-up table LUT_(OUT) stored in the ROM 112. As a result,the YMCK values corresponding to the respective L*, a*, b* values arecalculated (primary calculation of the patch color (L*, a*, b*)). Withreference to FIG. 10A and FIG. 10B, the color conversion look-up tableLUT_(OUT) for converting the L*, a*, b* values into the YMCK valuesbeing print parameters is described.

FIG. 10A and FIG. 10B show the concept of the color conversion look-uptable LUT_(OUT). FIG. 10A is the three-dimensional color conversionlook-up table LUT_(OUT) of the input color space (Lab color space). Inthe color conversion look-up table LUT_(OUT), cubes are arrayed at equalintervals on the Lab color space. In this case, the Lab color space is aCIE 1976 (L*, a*, b*) color space, but may also be a Hunter 1948 L, a, bcolor space. Each vertex (grid point) of the cube represents a position(L*, a*, b* values) on the Lab color space. In this case, L* representslightness, and a* and b* represent chromaticity. At the grid point, apatch color (YMCK values) corresponding to the L*, a*, b* values at thecorresponding position is allocated.

For example, in a case where L_(β)*, a_(β)*, b_(β)* on the grid pointare designated as the L*, a*, b* values for which conversion is desired,Y_(β), M_(β), C_(β), and K_(β) being the corresponding patch color (YMCKvalues) of the color conversion look-up table LUT_(OUT) are output.

In FIG. 10B, a table interpolation method is described. The L*, a*, b*values for which the color conversion is desired are in a regionsurrounded by a grid point 1 to a grid point 8. In a case wheredistances from the L*, a*, b* values to the grid points 1 to 8 are d1 tod8, respectively, the patch color (YMCK values) is calculated as followsin accordance with the distances to the respective grid points.Y=(Y ₁ /d ₁ +Y ₂ /d ₂ + . . . +Y ₈ /d ₈)/(1/d ₁+1/d ₂+ . . . +1/d ₈)M=(M ₁ /d ₁ +M ₂ /d ₂ + . . . +M ₈ /d ₈)/(1/d ₁+1/d ₂+ . . . +1/d ₈)C=(C ₁ /d ₁ +C ₂ /d ₂ + . . . +C ₈ /d ₈)/(1/d ₁+1/d ₂+ . . . +1/d ₈)K=(K ₁ /d ₁ +K ₂ /d ₂ + . . . +K ₈ /d ₈)/(1/d ₁+1/d ₂+ . . . +1/d ₈)

The color conversion look-up table LUT_(OUT) is stored in the ROM 112,and the conversion operation processing from the L*, a*, b* values tothe patch color (YMCK values) is performed by the CPU 114.

The CPU 114 performs calculation of the patch colors (YMCK values)(performs secondary selection) (Step S802). The CPU 114 specifies atwhich positions on the color conversion look-up table LUT_(OUT) (FIG.10A) stored in the ROM 112 L₀₀*, a₀₀*, b₀₀* to L₄₈*, a₄₈*, b₄₈* of thespecific color and the surrounding colors are located. After the CPU 114has confirmed the positions on the color conversion look-up tableLUT_(OUT), the CPU 114 selects the grid points having the smallestdistance among the surrounding grid points. The CPU 114 sets the YMCKvalues associated with the selected grid points as the calculationresults (secondary calculation of the patch color (L*, a*, b*)).

For example, in FIG. 10B, the values of L*, a*, b* for which the colorconversion is desired are in the region surrounded by the grid point 1to the grid point 8. The distances from the values of L*, a*, b* to thegrid points 1 to 8 are d1 to d8, respectively, and d1 has the smallestvalue. In this case, the YMCK values are calculated as follows.Y=Y ₁M=M ₁C=C ₁K=K ₁

The CPU 114 causes the printer 150 to create the color calibration chart501 of FIG. 7 based on the patch colors (YMCK values) calculated in theprocess steps of Step S801 and Step S802 (Step S803). The CPU 114performs color measurement of the created color calibration chart 501 bythe line sensor 301 and the spectroscopic sensor unit 315 (Step S804).

The line sensor 301 outputs the luminance values (RGB data) of therespective colors being the color measurement results to the colordetection processing unit 305. The color detection processing unit 305calculates the average luminance values (R_(A), G_(A), B_(A)) of therespective colors of RGB in the measurement region from the RGB dataacquired from the line sensor unit 312. The CPU 114 uses the colorconversion look-up table LUT_(IN) for converting the luminance values ofR, G, and B into L*, a*, b* to convert the average luminance values(R_(A), G_(A), B_(A)) into the L*, a*, b* values. The CPU 114 acquires98 Lab values as the color measurement results obtained by the linesensor unit 312. The 98 Lab values are L*, a*, b* values of L_(L_A00)*,a_(L_A00)*, b_(L_A00)* to L_(L_A48)*, a_(L_A48)*, b_(L_A48)*, andL_(L_P00)*, a_(L_P00)*, b_(L_P00)* to L_(L_P48)*, a_(L_P48)*,b_(L_P48)*.

The spectroscopic sensor 306 outputs the spectral data in themeasurement region of the color calibration chart 501 being the colormeasurement results to the color detection processing unit 305. Thespectral data is 98 L*, a*, b* values. Specifically, the spectral datais L_(S_A00)*, a_(S_A00)*, b_(S_A00)* to L_(S_A48)*, a_(S_A48)*,b_(S_A48)*, and L_(S_P00)*, a_(S_P00)*, b_(S_P00)* to L_(S_P48)*,a_(S_P48)*, b_(S_P48)*. The color detection processing unit 305calculates the L*, a*, b* values from the spectral data acquired fromthe spectroscopic sensor unit 315. The color detection processing unit305 outputs the calculated L*, a*, b* values to the CPU 114.

The CPU 114 selects, from the 98 L*, a*, b* values measured by thespectroscopic sensor 306, 49 items of data having values closest to thevalues of L₀₀*, a₀₀*, b₀₀* to L₄₈*, a₄₈*, b₄₈* calculated in Step S800(Step S805). The selected 49 L*, a*, b* values are represented byZ_(A00), Z_(B00), Z_(C00) to Z_(A48), Z_(B48), Z_(C48). Further, the CPU114 selects, from the color measurement data of the line sensor 301, 49L*, a*, b* values obtained in a case where the colors of the same patchimages as Z_(A00), Z_(B00), Z_(C00) to Z_(A48), Z_(B48), Z_(C48) aremeasured by the line sensor 301. The selected 49 L*, a*, b* values arerepresented by X_(A00), X_(B00), X_(C00) to X_(A48), X_(B48), X_(C48).

The CPU 114 generates the color calibration matrix M of the line sensor301 (Step S806). The CPU 114 calculates, through use of Z_(A00),Z_(B00), Z_(C00) to Z_(A48), Z_(B48), Z_(C48) and X_(A00), X_(B00),X_(C00) to X_(A48), X_(B48), X_(C48) as training data, the colorcalibration matrix M for calibrating the measurement result of the linesensor 301 by the following expression. The color calibration matrix Mis a 3×10 matrix. The CPU 114 stores the calculated color calibrationmatrix M into the RAM 113. As described above, the color calibrationmatrix M is obtained through the color calibration processing.

${{Matrix}X} = \begin{bmatrix}\begin{matrix}{X_{A00},X_{B00},X_{C00},} \\\begin{matrix}{{X_{A00}\hat{}2},{X_{B00}\hat{}2},{X_{C00}\hat{}2},} \\{{X_{A00}*X_{B00}},{X_{B00}*X_{C00}},{X_{C00}*X_{A00}},}\end{matrix}\end{matrix} & 1 \\\begin{matrix}{X_{A01},X_{B01},X_{C01},} \\\begin{matrix}{{X_{A01}\hat{}2},{X_{B01}\hat{}2},{X_{C01}\hat{}2},} \\{{X_{A01}*X_{B01}},{X_{B01}*X_{C01}},{X_{C01}*X_{A01}},}\end{matrix}\end{matrix} & 1 \\{\vdots} & \\{\vdots} & \\{\vdots} & \\\begin{matrix}{X_{A02},X_{B02},X_{C02},} \\\begin{matrix}{{X_{A02}\hat{}2},{X_{B02}\hat{}2},{X_{C02}\hat{}2},} \\{{X_{A02}*X_{B02}},{X_{B02}*X_{C02}},{X_{C02}*X_{A02}},}\end{matrix}\end{matrix} & 1\end{bmatrix}$ ${{Matrix}Z} = \begin{bmatrix}{Z_{A00},Z_{B00},Z_{C00}} \\{Z_{A01},Z_{B01},Z_{C01}} \\ \vdots \\ \vdots \\ \vdots \\{Z_{A48},Z_{B48},Z_{C48}}\end{bmatrix}$

where: X^(T) is a transpose matrix of the matrix X, and (X^(T)*X)⁻¹ isan inverse matrix of (X^(T)*X).

As described above, in the first embodiment, the color calibration charthaving printed thereon the patch images to be used for color calibrationof the line sensor 301 can be created through one time of printprocessing. As a result, the color calibration of the line sensor 301can be performed with high accuracy, and highly accurate colormeasurement of an image is allowed. Thus, a highly accurate colorinspection system can be achieved.

Second Embodiment

A configuration of an image forming apparatus 100 in a second embodimentof the present disclosure is similar to that in the first embodiment.The second embodiment is different from the first embodiment in thecontents of the color calibration processing, but other parts in thesecond embodiment are the same as those in the first embodiment. Thedifferent parts are described.

<Color Calibration Processing>

The color calibration processing of Step S602 of FIG. 6 is described.FIG. 11 is a diagram of an example of a color calibration chart to beused in the color calibration processing of the line sensor unit 312. Acolor calibration chart 501 is created by printing 49 patch images 504as the detection image on a recording sheet that is long in thesub-scanning direction. The patch images 504 are arranged in 7 rows and7 columns in the main scanning direction and the sub-scanning direction,respectively. At a left end of the color calibration chart 501 in themain scanning direction, a margin 502 is provided. On the right side ofthe margin 502, a black trigger patch 503 is provided. On the right sideof the trigger patch 503, the 49 patch images 504 are provided.

The 49 patch images 504 for color calibration are images having imagedensity values corresponding to the specific color L₀₀*, a₀₀*, b₀₀* andthe L*, a*, b* values of surrounding colors calculated as valuesseparated by predetermined color differences from the specific colorL₀₀*, a₀₀*, b₀₀*. In FIG. 11 , the middle patch image is an image havingthe image density values of the specific color L₀₀*, a₀₀*, b₀₀*. Theimage density values are set for each of the colors of yellow (Y),magenta (M), cyan (C), and black (K). In this case, the image densityvalues are referred to as “YMCK values.” The positions at which thepatch images 504 of the color calibration chart 501 are formed are notlimited to those of FIG. 11 .

FIG. 12 is a flow chart for illustrating the color calibrationprocessing. FIG. 13 is an explanatory diagram of a method of calculatingL*, a*, b* of the surrounding colors of the specific color.

The CPU 114 calculates L*, a*, b* of the surrounding colors from thespecific color L₀₀*, a₀₀*, b₀₀* (Step S900). For the calculation, theCPU 114 first acquires the specific color L₀₀*, a₀₀*, b₀₀*, and thecolor inspection threshold value Cth from the RAM 113. The CPU 114calculates the surrounding colors separated by predetermined colordifferences from the specific color L₀₀*, a₀₀*, b₀₀*. The surroundingcolors are selected so that the range of the predetermined colordifferences ranges across the color inspection threshold value Cth(ΔEmin<Cth<ΔEmax).

For example, as illustrated in FIG. 13 , 48 surrounding colors areselected. FIG. 13 shows an example of a case in which the colorinspection threshold value Cth is “5”. The CPU 114 selects, as thepredetermined color differences, ΔE00=2, 4 smaller than ΔE00=5 andΔE00=6, 8, 10, 12 larger than ΔE00=5 so that the ΔE00 ranges acrossΔE00=5. The CPU 114 calculates L*, a*, b* of the following 48surrounding colors corresponding to the selected ΔE00.

-   -   Surrounding color 01 to surrounding color 08 separated in color        by color difference ΔE00=2        -   L*, a*, b*=L₀₁*, a₀₁*, b₀₁* to L₀₈*, a₀₈*, b₀₈*    -   Surrounding color 09 to surrounding color 16 separated in color        by color difference ΔE00=4        -   L*, a*, b*=L₀₉*, a₀₉*, b₀₀* to L₁₆*, a₁₆*, b₁₆*    -   Surrounding color 17 to surrounding color 24 separated in color        by color difference ΔE00=6        -   L*, a*, b*=L₁₇*, a₁₇*, b₁₇* to L₂₄*, a₂₄*, b₂₄*    -   Surrounding color 25 to surrounding color 32 separated in color        by color difference ΔE00=8        -   L*, a*, b*=L₂₅*, a₂₅*, b₂₅* to L₃₂*, a₃₂*, b₃₂*    -   Surrounding color 33 to surrounding color 40 separated in color        by color difference ΔE00=10        -   L*, a*, b*=L₃₃*, a₃₃*, b₃₃* to L₄₀*, a₄₀*, b₄₀*    -   Surrounding color 41 to surrounding color 48 separated in color        by color difference ΔE00=12        -   L*, a*, b*=L₄₁*, a₄₁*, b₄₁* to L₄₈*, a₄₈*, b₄₈*

The CPU 114 calculates patch colors (Y, M, C, K) being colors of thepatch images to be used in the color calibration chart 501 (Step S901).The CPU 114 converts L₀₀*, a₀₀*, b₀₀* to L₄₈*, a₄₈*, b₄₈* based on thecolor conversion look-up table LUT_(OUT) stored in the ROM 112. As aresult, the YMCK values corresponding to the respective L*, a*, b*values are calculated (calculation of the patch color (L*, a*, b*)). Thecolor conversion look-up table LUT_(OUT) for converting the L*, a*, b*values into the YMCK values being the print parameter is as describedwith reference to FIG. 10A and FIG. 10B in the first embodiment.

The CPU 114 causes the printer 150 to create the color calibration chart501 of FIG. 11 based on the patch colors (YMCK values) calculated in theprocess step of Step S901 (Step S902). The CPU 114 performs colormeasurement of the created color calibration chart 501 by the linesensor 301 and the spectroscopic sensor unit 315 (Step S903).

The line sensor 301 outputs the luminance values (RGB data) of therespective colors being the color measurement results to the colordetection processing unit 305. The color detection processing unit 305calculates the average luminance values (R_(A), G_(A), B_(A)) of therespective colors of RGB in the measurement region from the RGB dataacquired from the line sensor unit 312. The CPU 114 uses the colorconversion look-up table LUT_(IN) for converting the luminance values ofR, G, and B into L*, a*, b* to convert the average luminance values(R_(A), G_(A), B_(A)) into the L*, a*, b* values. The CPU 114 acquires49 L*, a*, b* values of L_(L_A00)*, a_(L_A00)*, b_(L_A00)* toL_(L_A48)*, a_(L_A48)*, b_(L_A48)*, as the color measurement resultsobtained by the line sensor unit 312.

The spectroscopic sensor 306 outputs the spectral data of the colorcalibration chart 501 being the color measurement results to the colordetection processing unit 305. The color detection processing unit 305acquires 49 L*, a*, b* values of L_(S_A00)*, a_(S_A00)*, b_(S_A00)* toL_(S_A48)*, a_(S_A48)*, b_(S_A48)*, as the spectral data. The colordetection processing unit 305 calculates the L*, a*, b* values from thespectral data acquired from the spectroscopic sensor unit 315. The colordetection processing unit 305 outputs the calculated L*, a*, b* valuesto the CPU 114.

The 49 L*, a*, b* values of the spectral data acquired by the colordetection processing unit 305 are represented by Z_(A00), Z_(B00),Z_(C00) to Z_(A48), Z_(B48), Z_(C48). The L*, a*, b* values obtained ina case where the colors of the same patch images as Z_(A00), Z_(B00),Z_(C00) to Z_(A48), Z_(B48), Z_(C48) are measured by the line sensor 301are represented by X_(A00), X_(B00), X_(C00) to X_(A48), X_(B48),X_(C48).

The CPU 114 generates the color calibration matrix M of the line sensor301 (Step S904). The CPU 114 calculates, through use of Z_(A00),Z_(B00), Z_(C00) to Z_(A48), Z_(B48), Z_(C48) and X_(A00), X_(B00),X_(C00) to X_(A48), X_(B48), X_(C48) as training data, the colorcalibration matrix M for calibrating the measurement result of the linesensor 301. The color calibration matrix M is a 3×10 matrix. The CPU 114stores the calculated color calibration matrix M into the RAM 113. Thecalculation of the color calibration matrix M is as described in thefirst embodiment.

As described above, in the second embodiment, the printer 150 prints, onthe recording sheet, the specific color and the surrounding colorslocated with predetermined color differences from the specific color asthe detection image so that the color calibration chart is created. Thecolor calibration chart is read by the reader 160. Based on the resultof reading the color calibration chart by the reader 160, the colorconversion table of RGB→Lab for the specific color is created. As aresult, the conversion accuracy from RGB to Lab with respect to colorsin the vicinity of the specific color is improved, and a highly accuratecolor inspection system can be achieved.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2021-038570, filed Mar. 10, 2021, and Japanese Patent Application No.2021-038564, filed Mar. 10, 2021, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. An information processing device comprising: amemory configured to store color information related to a color to beinspected in an image, wherein the image is formed by an image formingapparatus; and a controller configured to: acquire user instructioninformation related an acceptable range of color difference forinspection of the color; output test image data for forming a pluralityof test images based on the color information and the user instructioninformation, the plurality of test images including: (i) a first testimage, a color difference between the color to be inspected and a colorof the first test image being within the acceptable range, and (ii) asecond test image, a color difference between the color to be inspectedand a color of the second test image being out of the acceptable range;acquire first data related to the plurality of test images, wherein thefirst data is output by a first sensor which detects a first number oflights, each with a different wavelength, included in the reflectedlight from the plurality of test images; acquire second data related tothe plurality of test images, wherein the second data is output by asecond sensor, which detects a second number of lights, each with adifferent wavelength, included in the reflected light from the pluralityof test images, the second number being more than the first number;generate, based on the first data and the second data, a conversioncondition; acquire third data related to the color to be inspected in animage formed by the image forming apparatus, wherein the third data isoutput by the first sensor; convert, based on the generated conversioncondition, the third data; and determine, based on converted third dataand the color information and the acceptable range, a color shift withrespect to the color in the image formed by the image forming apparatus.2. The information processing device according to claim 1, wherein thecontroller is configured to determine a color difference based on thecolor information and the converted third data, and compare the colordifference with the acceptable range, and determine the color shiftbased on a comparison of the color difference with the acceptable range.3. The information processing device according to claim 2, wherein thecontroller is configured to output a notification of an error in a casewhere the color difference is out of the acceptable range.
 4. Theinformation processing device according to claim 1, wherein thewavelengths of the light detected by the first sensor include 630 nm,530 nm, and 440 nm.
 5. The information processing device according toclaim 1, wherein the first data is luminance data of the plurality oftest images, wherein the second data is spectroscopic data of theplurality of test images, and wherein the third data is luminance dataof the color to be inspected.
 6. The information processing deviceaccording to claim 1, wherein the first data is a detection result ofthe reflected light of red, blue, and green from the plurality of testimages, wherein the second data is a detection result of L*, a*, b*based on the reflected light from the plurality of test images, whereinthe first data is a detection result of the reflected light of red,blue, and green from the color to be inspected.
 7. A method ofcontrolling an image forming apparatus that forms an image on a sheet,the method comprising: a first acquisition step of acquiring colorinformation related to a color to be inspected in an image; a secondacquisition step of acquiring user instruction information related anacceptable range of color difference for inspection of the color; a testprint step of printing the plurality of test images based on the colorinformation and the user instruction information, the plurality of testimages including: (i) a first test image, a color difference between thecolor to be inspected and a color of the first test image being withinthe acceptable range, and (ii) a second test image, a color differencebetween the color to be inspected and a color of the second test imagebeing out of the acceptable; a first detecting step of detecting theplurality of test images by a first sensor, the first sensor detects afirst number of lights, each with a different wavelength, included in areflected light from the plurality of test images; a second detectingstep of detecting the plurality of test images by a second sensor,wherein the second sensor detects a second number of lights, each with adifferent wavelength, included in the reflected light from the pluralityof test images, the second number being more than the first number; ageneration step of generating, based on a detecting result of theplurality of test images detected by the first sensor and a detectingresult of the plurality of test images detected by the second sensor, aconversion condition; a print step of printing the image; a thirddetecting step of detecting the color to be inspected in the image bythe first sensor; a conversion step of converting a detecting result ofthe color to be inspected in the image detected by the first sensorbased on the generated conversion condition; and a determination step ofdetermining, based on the converted detecting result of the color to beinspected in the image detected by the first sensor and the colorinformation and the acceptable range, a color shift with respect to thecolor in the image formed by the image forming apparatus.
 8. The methodof controlling an image forming apparatus according to claim 7, furthercomprising a notification step of outputting a notification of an errorin a case where the color difference is out of the acceptable range. 9.The method of controlling an image forming apparatus according to claim7, the determination step includes: a first determination step ofdetermining a color difference based on the color information and theconverted detecting result of the color to be inspected in the imagedetected by the first sensor, and a comparison step of comparing thecolor difference with the acceptable range, and a second determinationstep of determining the color shift based on a comparison of the colordifference with the acceptable range.
 10. The method of controlling animage forming apparatus according to claim 7, wherein the detectionresult of the plurality of test images detected by the first sensor isluminance of the plurality of test images, wherein the detection resultof the plurality of test images detected by the second sensor is colorvalues of the plurality of test images, and wherein the detection resultof the color to be inspected detected by the third sensor is luminanceof the color to be detected.
 11. The method of controlling an imageforming apparatus according to claim 7, wherein the detection result ofthe plurality of test images detected by the first sensor is a detectionresult of the reflected light of red, blue, and green from the pluralityof test images, wherein the detection result of the plurality of testimages detected by the second sensor is a detection result of L*, a*, b*based on the reflected light from the plurality of test images, andwherein the detection result of the color to be inspected detected bythe third sensor is a detection result of the reflected light of red,blue, and green from the color to be inspected.